Small-Scale Experiments Completed for Heat Transfer Through Walls Project
Small-scale experiments for UL’s Fire Safety Research Institute (FSRI) Heat Transfer and Fire Damage Patterns on Walls for Fire Model Validation research project were completed in early October. The experiments were the first in a two-part series focusing on heat transfer and fire damage patterns on walls and fire model validation to support fire investigation applications. Led by FSRI research engineer, Matt DiDomizio, as part of a two-year research grant funded by the National Institute of Justice (NIJ), the small-scale tests were designed to validate a novel technique for measurement of field heat flux over the surface of a fire-exposed wall.
Three types of plate heat flux sensors, measuring 2' by 2' in size, were developed for these experiments, which included:
- a thin 22-gauge stainless steel plate coated in a high-temperature, high-emissivity paint mounted within an aluminum frame lined with ceramic fiber insulation;
- a thick 14-gauge stainless steel plate coated in a high-temperature, high-emissivity paint mounted within an aluminum frame lined with ceramic fiber insulation; and
- a thin 22-gauge stainless steel plate coated in a high-temperature, high-emissivity paint mounted within an aluminum frame containing a water-cooled copper bracket, which produced fixed-temperature boundary conditions on the edges of the plate.
Plate sensors were positioned in front of a vertically-aligned propane-fired radiant panel. A grid of thermocouples, spaced evenly at 8” vertically and horizontally, was positioned on the exposed and unexposed sides of the plate sensors to measure gas temperatures adjacent to the plate. Infrared thermography was used to obtain high-speed non-contact measurements of the surface temperature over the unexposed side of the plates. Initially a heat shield was placed between the plate sensors and the radiant panel while the burner stabilized. After 60 seconds of stabilization the heat shield was rapidly removed to initiate a step exposure. After approximately 15 minutes of exposure, the heat shield was replaced to end the experiment. Identical tests were also performed with Schmidt-Boelter total heat flux and radiometer gauges to obtain a performance baseline.
“This first round of experiments met all expectations,” said DiDomizio. “We anticipate the upcoming large-scale experiments to further validate this method for developing estimates of field heat flux on a fire-exposed surface, in addition to obtaining important heat transfer and fire damage pattern measurements on walls subjected to these exposures.”
Large-scale experiments for the Heat Transfer and Fire Damage Patterns on Walls for Fire Model Validation project will begin in December at the Bureau of Alcohol, Tobacco, Firearms and Explosives - Fire Research Laboratory (ATF-FRL) in Beltsville, MD. The primary output of this work will be a well-documented and publicly available dataset, report, and analysis. The experimentation is expected to produce validation data for heat transfer and fire damage patterns on walls exposed to fires. Property data will also be collected for the materials involved, such as insulation, steel, and gypsum wallboard.